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Subject[PATCH v2 1/3] dell-wmi: Stop storing pointers to DMI tables
Date
The dmi_walk function maps the DMI table, walks it, and unmaps it.
This means that the dell_bios_hotkey_table that find_hk_type stores
points to unmapped memory by the time it gets read.

I've been able to trigger crashes caused by the stale pointer a
couple of times, but never on a stock kernel.

Fix it by generating the keymap in the dmi_walk callback instead of
storing a pointer.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---

Notes:
Changes from v1:
- Rename handle_dmi_table to handle_dmi_entry (Jean)
- Remove useless assignment to results->err (Jean)

drivers/platform/x86/dell-wmi.c | 68 +++++++++++++++++++++++++----------------
1 file changed, 41 insertions(+), 27 deletions(-)

diff --git a/drivers/platform/x86/dell-wmi.c b/drivers/platform/x86/dell-wmi.c
index b6f193b07566..5c0d037fcd40 100644
--- a/drivers/platform/x86/dell-wmi.c
+++ b/drivers/platform/x86/dell-wmi.c
@@ -114,7 +114,10 @@ struct dell_bios_hotkey_table {

};

-static const struct dell_bios_hotkey_table *dell_bios_hotkey_table;
+struct dell_dmi_results {
+ int err;
+ struct key_entry *keymap;
+};

/* Uninitialized entries here are KEY_RESERVED == 0. */
static const u16 bios_to_linux_keycode[256] __initconst = {
@@ -315,20 +318,34 @@ static void dell_wmi_notify(u32 value, void *context)
kfree(obj);
}

-static const struct key_entry * __init dell_wmi_prepare_new_keymap(void)
+static void __init handle_dmi_entry(const struct dmi_header *dm,
+ void *opaque)
{
- int hotkey_num = (dell_bios_hotkey_table->header.length - 4) /
- sizeof(struct dell_bios_keymap_entry);
+ struct dell_dmi_results *results = opaque;
+ struct dell_bios_hotkey_table *table;
struct key_entry *keymap;
- int i;
+ int hotkey_num, i;
+
+ if (results->err || results->keymap)
+ return; /* We already found the hotkey table. */
+
+ if (dm->type != 0xb2 || dm->length <= 6)
+ return;
+
+ table = container_of(dm, struct dell_bios_hotkey_table, header);
+
+ hotkey_num = (table->header.length - 4) /
+ sizeof(struct dell_bios_keymap_entry);

keymap = kcalloc(hotkey_num + 1, sizeof(struct key_entry), GFP_KERNEL);
- if (!keymap)
- return NULL;
+ if (!keymap) {
+ results->err = -ENOMEM;
+ return;
+ }

for (i = 0; i < hotkey_num; i++) {
const struct dell_bios_keymap_entry *bios_entry =
- &dell_bios_hotkey_table->keymap[i];
+ &table->keymap[i];

/* Uninitialized entries are 0 aka KEY_RESERVED. */
u16 keycode = (bios_entry->keycode <
@@ -357,11 +374,12 @@ static const struct key_entry * __init dell_wmi_prepare_new_keymap(void)

keymap[hotkey_num].type = KE_END;

- return keymap;
+ results->keymap = keymap;
}

static int __init dell_wmi_input_setup(void)
{
+ struct dell_dmi_results dmi_results = {};
int err;

dell_wmi_input_dev = input_allocate_device();
@@ -372,20 +390,26 @@ static int __init dell_wmi_input_setup(void)
dell_wmi_input_dev->phys = "wmi/input0";
dell_wmi_input_dev->id.bustype = BUS_HOST;

- if (dell_new_hk_type) {
- const struct key_entry *keymap = dell_wmi_prepare_new_keymap();
- if (!keymap) {
- err = -ENOMEM;
- goto err_free_dev;
- }
+ err = dmi_walk(handle_dmi_entry, &dmi_results);
+ if (err)
+ goto err_free_dev;

- err = sparse_keymap_setup(dell_wmi_input_dev, keymap, NULL);
+ if (dmi_results.err) {
+ err = dmi_results.err;
+ goto err_free_dev;
+ }
+
+ if (dmi_results.keymap) {
+ dell_new_hk_type = true;
+
+ err = sparse_keymap_setup(dell_wmi_input_dev,
+ dmi_results.keymap, NULL);

/*
* Sparse keymap library makes a copy of keymap so we
* don't need the original one that was allocated.
*/
- kfree(keymap);
+ kfree(dmi_results.keymap);
} else {
err = sparse_keymap_setup(dell_wmi_input_dev,
dell_wmi_legacy_keymap, NULL);
@@ -412,15 +436,6 @@ static void dell_wmi_input_destroy(void)
input_unregister_device(dell_wmi_input_dev);
}

-static void __init find_hk_type(const struct dmi_header *dm, void *dummy)
-{
- if (dm->type == 0xb2 && dm->length > 6) {
- dell_new_hk_type = true;
- dell_bios_hotkey_table =
- container_of(dm, struct dell_bios_hotkey_table, header);
- }
-}
-
static int __init dell_wmi_init(void)
{
int err;
@@ -431,7 +446,6 @@ static int __init dell_wmi_init(void)
return -ENODEV;
}

- dmi_walk(find_hk_type, NULL);

err = dell_wmi_input_setup();
if (err)
--
2.5.0

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